Vehicles are comprised of a host of independent and interdependent systems. Primary and secondary controllers process various signals transmitted by physical sensors to determine the proper functioning of the sensors and related onboard systems. A common cost reduction technique is the replacement of some of the physical sensors with virtual sensors, i.e., software-based estimators or inferred logic values. Virtual sensors may reduce the cost and packaging associated with each physical sensor that is replaced, along with its associated harness, as well as the required sensor diagnostics for the replaced sensor. However, software-based estimators may be less than optimal under certain conditions, e.g., during a sensor redesign or for certain types of high-voltage electrical motor sensors.
In a typical hybrid vehicle, diagnostic logic is hardcoded such that every high-voltage power inverter and electric motor combination requires three different phase inverter temperature sensors, which are typically configured as thermistors, and a motor winding thermistor. The diagnostic logic ordinarily must be reprogrammed whenever one of the thermistors is eliminated. As a result, conventional temperature diagnostic logic cannot adequately diagnose more than one severely drifted thermistor.